Late last year, Downton Abbey writer Julian Fellowes said he was planning to introduce a black or Indian character to the programme, to "open the show up ethnically".

Other new characters for the forthcoming series will include Sir John Bullock, "who must be able to act drunk", and Lord Anthony Gillingham, a "good-looking, very charismatic" love interest for Lady Mary Crawley (played by Golden Globe-nominee Michelle Dockery).

Since it began in 2010, the drama, set in a fictional Yorkshire country estate, has won multiple Emmy awards, and become most watched drama series on ITV and American broadcaster PBS. Last month its cast – which includes Hugh Bonneville and Dame Maggie Smith – won the Screen Actors Guild awardfor outstanding performance by an ensemble in a drama series.